Sometimes circuits are expected to be operated over a range of operating conditions. For example, circuits that are used in mobile devices may be expected to be operated over a range of supply voltages and temperatures, and during the manufacturing of those circuits a range of process variations may result. Changing the operating conditions can change the electrical characteristics of circuit elements, which, in turn, can change the behavior of the circuit. It is desirable to design circuits that can continue to operate with maximum margins across the manufactured variation space even when the operating conditions change.